Polyphosphoinositide hydrolysis and protein kinase C activation in guinea pig tracheal smooth muscle cells in culture by leukotriene D4 involve a pertussis toxin sensitive G-protein

Leukotriene D4 (LTD4) at concentrations greater than 1 nM induced phosphatidylinositol bisphosphate (PIP2) hydrolysis and protein kinase C (PKC) activation in primary culture of airway smooth muscle cells. Within seconds of activation, an increase in inositol 1,4,5-trisphosphate (IP3) was observed reaching a maximum at 5 min. The level of IP3 decreased after 5 min and was followed by an increase in inositol 1,4-bisphosphate (IP2) and inositol 1-monophosphate (IP1). LTD4-induced PIP2 hydrolysis was inhibited by 1 h pretreatment of cells with 10 micrograms/ml of pertussis toxin (PTX). LTD4 activated both soluble and particulate forms of PKC by 2-3-fold. The LTD4-induced PKC activation was blocked by treatment of cells with PTX, suggesting the involvement of a PTX-sensitive G-protein. To assess the involvement of G(i) in smooth muscle cell receptor activation, the modulation of adenylyl cyclase activity was investigated. LTD4 did not stimulate cAMP formation in smooth muscle cells, and did not inhibit forskolin-induced cAMP formation. These data suggest that the LTD4 receptor in airway smooth muscle cells is coupled to a PTX-sensitive G-protein, possibly G(o).